Area Forecast Discussion
Issued by NWS Twin Cities, MN

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KMPX 211237
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
737 AM CDT SUN SEP 21 2014

.UPDATE...
ISSUED AT 650 AM CDT SUN SEP 21 2014

UPDATED TO INCLUDE 12Z AVIATION DISCUSSION BELOW.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 425 AM CDT SUN SEP 21 2014

TODAY-TONIGHT...SFC ANALYSIS SHOWS A CDFNT PUSHING ACRS LAKE MI
INTO LOWER MI WITH A SECONDARY CDFNT DRAPED FROM CENTRAL
MANITOBA PROVINCE THRU THE NRN GREAT LAKES INTO QUEBEC PROVINCE.
THE FIRST CDFNT WAS RESPONSIBLE FOR THE STRONG/SEVERE TSTMS THAT
PASSED THRU THIS REGION YDA...WHILE THE SECOND CDFNT IS MORE
REFLECTIVE OF THE UPR LVL VORT MAX DROPPING SEWD FROM S-CENTRAL
CANADA. CYCLONIC FLOW ARND THIS UPR VORT WITHIN COLD AIR ALOFT AND
LINGERING DEEP MOISTURE WILL PRODUCE SCTD SHWRS OVER WRN WI INTO
FAR ERN MN THRU THE FIRST HALF OF TDA. NO SEVERE WX WILL COME FROM
THIS...AND HIGHLY LIKELY THAT NO TSTMS WILL DEVELOP WITH A MUCH
MORE STABLE ATMOS IN PLACE. SO...HAVE KEPT POPS NO HIGHER THAN CHC
CATEGORY FROM DAYBREAK ON AS COVERAGE NOT EXPECTED TO BE ALL THAT
GREAT...AND QPF WILL BE QUITE LIGHT...GENERALLY ONLY UP TO A FEW
HUNDREDTHS TO BE RECEIVED. ANY AND ALL PRECIP SHOULD DISSIPATE AND
SHIFT OFF TO THE E BY MIDDAY WITH GRADUAL CLEARING EXPECTED
THEREAFTER AS HIGH PRES SLOWLY ARRIVES FROM THE W. DEEP DRY NW
FLOW FROM THE SFC UPWARD WILL PROMOTE CLEARING SKIES THIS EVENING
THRU THE OVERNIGHT HRS. THE ONLY QUESTION WILL BE THE COVERAGE OF
FOG OVERNIGHT AS CAA KICKS INTO HIGH GEAR WHILE WINDS DROP OFF
UNDER THE CLEARING SKIES. CROSSOVER TEMPS ARE CLOSE SO IT MAY WELL
BE A MATTER OF HOW MUCH MOISTURE CAN BE SCOURED OUT BEFORE THE
NIGHTLY INVERSION SETS IN. HAVE OPTED TO INCLUDE PATCHY FOG FOR
NRN AND ERN PORTIONS OF THE CWFA WHERE WINDS ARE MOST LIKELY TO GO
CALM AND WHERE COLDEST TEMPS ARE EXPECTED. WITH RESPECT TO THE
CAA...HIGHS TDA WILL BE NOTICEABLY COOLER THAN SATURDAY WITH HIGHS
RANGING FROM THE LWR 60S IN WRN WI TO THE UPR 60S TO ARND 70 IN
WRN MN. FOR TNGT...LOWS OUTSIDE THE TWIN CITIES METRO WILL DROP TO
THE LOW-MID 40S...WITH MIN TEMPS CLOSE TO 50 WITHIN THE TC METRO.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 425 AM CDT SUN SEP 21 2014

THE UPPER MIDWEST WILL FIND ITSELF ON THE WARM SIDE OF A HIGHLY
AMPLIFIED UPPER LEVEL PATTERN WHICH WILL LEAD TO TEMPERATURES THAT
WILL BE WELL ABOVE THE SEASONAL AVERAGE FOR LATE SEPTEMBER. DRY
WEATHER IS EXPECTED ASIDE FROM SCATTERED SHOWERS LATE TUESDAY
THROUGH WEDNESDAY.

EARLY MORNING WATER VAPOR IMAGERY WITH GFS 21.00 500MB HEIGHTS AND
WINDS SHOWED A DIGGING TROUGH OVER THE NORTHWEST PACIFIC WITH A
RIDGING OVER THE CANADIAN ROCKIES. MEANWHILE A WEAKENING OCCLUDED
PV ANOMALY WAS SITUATED ACROSS SOUTHERN CALIFORNIA...AND THIS
WILL BE THE FOCUS FOR PRECIP CHANCES EARLY IN THE PERIOD. FORECAST
SOUNDINGS SHOW DRY AIR IN THE LOWER LEVELS...SO MAY SEE MORE MID-
LEVEL SATURATION/CLOUDS THAN ACTUAL PRECIP. THEREFORE BROKE UP THE
POPS INTO 6HR BLOCKS TO INCREASE THE TEMPORAL RESOLUTION.
ALSO...FORECAST SOUNDINGS DO NOT SHOW ELEVATED INSTABILITY...SO
HAVE LOW CONFIDENCE IN UPRIGHT CONVECTION AND AS RESULT REMOVED
THE THUNDER MENTION FROM THE WEATHER GRIDS.

LOOKING AHEAD...WARM AIR MOVES ACROSS THE REGION AS THE UPPER
LEVEL PATTERN AMPLIFIES. WAS TEMPTED TO INCREASE POPS WELL ABOVE
GUIDANCE...BUT THERE ARE TWO VARIABLES THAT PREVENTED THIS. FIRST
OF ALL...FORECAST MODELS HINT AT A WEAK WAVE CUTTING OFF OVER THE
CORN BELT...AND THIS COULD LEAD TO MID/UPPER LEVEL CLOUDS WHICH
WILL SEVERELY LIMIT AFTERNOON HEATING. SECONDLY...SURFACE WINDS
MAY CONTAIN A SLIGHT EASTERLY COMPONENT. FORECAST SOUNDINGS SHOW
AFTERNOON MIXING WITH WINDS EVENTUALLY BECOMING 180-190DEG...BUT
IF CLOUDS MOVE IN THEN THE BOUNDARY LAYER MIXING WILL BE LESS THAN
CURRENTLY FORECAST. SINCE IT IS ONLY SUNDAY...HAVE PLENTY OF TIME
TO RAISE TEMPERATURES FOR THE LATTER HALF OF THE WEEK...SO WAS
CONTENT TO STICK WITH THE HIGHER END OF GUIDANCE...RATHER THAN
EXCEEDING IT.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 650 AM CDT SUN SEP 21 2014

CYCLONIC FLOW AROUND A DEPARTING UPPER LEVEL LOW SHOWING UP NICELY
ON WV IMAGERY THIS MORNING IS BRINGING DOWN MVFR CEILINGS TO MOST
TAF SITES THIS MRNG...PLUS A BATCH OF SHOWERS GLIDING SWD OVER WRN
WI. THE -SHRA WILL BE IN-AND-OUT OF BOTH KRNH AND KEAU FOR THE
FIRST 2-3 HRS OF THE 21/12Z TAFS ALONG WITH FAIRLY STOIC MVFR CIGS
THRU MIDDAY WHILE THE REMAINING SITES /EXCEPT KRWF WHICH LOOKS TO
REMAIN VFR/ WILL EXPERIENCE MVFR CIGS FOR AT LEAST THE FIRST FEW
HRS OF THIS TAF SET. AS THE UPPER LOW CONTINUES TO MOVE AWAY TO
THE E AND HIGH PRES ARRIVES FROM THE W...SKIES WILL CLEAR OUT THIS
AFTN INTO THIS EVE...EVENTUALLY RESULTING IN SKC. BREEZY/GUSTY NW
WINDS WILL PERSIST FOR MUCH OF THE DAY THEN DROP OFF STEADILY LATE
DAY TO NEAR CALM OVERNIGHT.

KMSP...CEILINGS BOUNCING BETWEEN SCT020 AND BKN020 FOR THE FIRST
FEW HRS...THEN VFR WITH GRADUALLY LIFTING CEILINGS THROUGHOUT THE
DAY. NO PRECIP EXPECTED AT KMSP...BUT WILL NOT BE FAR OFF TO THE E
THRU LATE MRNG. CLOUD COVER TO GRADUALLY SCATTER OUT LATE
DAY...EVENTUALLY ENDING UP VFR THIS EVE THRU OVERNIGHT.

/OUTLOOK FOR KMSP/
MON...VFR. WINDS W 5-10 KTS.
TUE...VFR. WINDS S 10 KTS.
WED...VFR WITH MVFR/SHRA/TSRA POSSIBLE. WINDS S 10-15 KTS.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&

$$

UPDATE...JPC
SHORT TERM...JPC
LONG TERM...JRB
AVIATION...JPC






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.